Optical display system

ABSTRACT

An optical display system includes a polarizer, an integrated back light unit optically connected to a first face of the polarizer and a display comprising an array of pixels optically connected to a second face of the polarizer. The first face of the polarizer and the second face of the polarizer are not parallel and the polarizer is configured to direct light from the integrated back light unit to the display.

FIELD

The embodiments of the invention are directed generally to semiconductorlight emitting devices, such as light emitting diodes (LED), andspecifically to a projection display containing integrated back lightLED unit.

BACKGROUND

LEDs are used in electronic displays, such as liquid crystal displays inlaptops or LED televisions. Conventional LED units are fabricated bymounting LEDs to a substrate, encapsulating the mounted LEDs and thenoptically coupling the encapsulated LEDs to an optical waveguide. Theconventional LED units may suffer from poor optical coupling.

SUMMARY

An embodiment is drawn to an optical display system including apolarizer, an integrated back light unit optically connected to a firstface of the polarizer and a display comprising an array of pixelsoptically connected to a second face of the polarizer. The first face ofthe polarizer and the second face of the polarizer are not parallel andthe polarizer is configured to direct light from the integrated backlight unit to the display.

Another embodiment is drawn to a method of making an optical displaysystem including optically connecting integrated back light unit to afirst face of a polarizer and optically connecting display comprising anarray of pixels to a second face of the polarizer. The first face of thepolarizer and the second face of the polarizer are not parallel andwherein the polarizer is configured to direct light from the integratedback light unit to the display.

Another embodiment is drawn to a method of projecting an image,including providing plural colors of light from an integrated back lightunit to a first face of a polarizer, providing the light from a secondface of the polarizer to an array of pixels of a display, and projectingthe image from the array of pixels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a side cross sectional view of anintegrated back light unit according to an embodiment.

FIG. 2 is a schematic illustration of a side cross sectional view of anintegrated back light unit according to another embodiment.

FIGS. 3A-3D illustrate a light emitting device according to anembodiment including: (A) a plan view; (B) a side cross sectional viewthrough section J-J of FIG. 3(F); (C) a close up of the plan view ofFIG. 3(A); and (D) a close up of the cross sectional view of FIG. 3(B).

FIG. 4A is a plan view of a portion of an integrated back light unitaccording to an embodiment with die bonded LEDs.

FIG. 4B is a side cross sectional view of light emitting device for anintegrated back light unit according to an embodiment. The lightemitting device includes an optical launch with metallized side faces.

FIG. 4C is a plan view of an integrated back light unit according to anembodiment with wire bonded LEDs.

FIG. 4D is a side cross sectional view of an integrated back light unitaccording to an embodiment.

FIG. 4E is a plan view of an integrated back light unit according to anembodiment.

FIG. 4F is a perspective view of an integrated back light unitillustrated in FIG. 4E.

FIG. 4G is a side cross sectional view of an integrated back light unitillustrated in FIG. 4E.

FIG. 4H is a side cross sectional close up of portion B of theintegrated back light unit illustrated in FIG. 4G.

FIGS. 5A-5C illustrate steps in a method of fabricating an integratedback light unit according to an embodiment. FIG. 5D illustrates analternative integrated back light unit according to an embodiment.

FIGS. 6A-6D illustrate steps in another method of fabricating anintegrated back light unit according to an embodiment. FIG. 6Eillustrates an alternative integrated back light unit according to anembodiment.

FIGS. 7A-7D illustrate an alternative method of fabricating anintegrated back light unit according to an embodiment. FIG. 7Eillustrates an alternative integrated back light unit according to anembodiment.

FIG. 8 is a circuit diagram illustrating a circuit configurationallowing individual control of LEDs in an array of LEDs.

FIG. 9 is a ray diagram illustrating the effect of misalignment in anintegrated back light unit according to an embodiment.

FIG. 10 is a plot of LED distribution as a function of couplingefficiency.

FIGS. 11A-11B illustrate alternative embodiments of integrated backlight units.

FIG. 12 is a schematic illustration of a side cross sectional view of anintegrated back light unit according to an embodiment.

FIG. 13A is a schematic illustration of a side cross sectional view ofan integrated back light unit illustrating the location of a hot spot inbrightness.

FIG. 13B is a schematic illustration of a side cross sectional view ofan integrated back light unit according to another embodiment.

FIGS. 14A and 14B are schematic illustrations of alternative embodimentsof integrated back light units with embedded dye and/or phosphorparticles.

FIGS. 15A and 15B are schematic illustrations of embodiments ofintegrated back light units with wavelength converting materials.

FIG. 16 is a schematic illustration of a method of making integratedback light units according to an embodiment.

FIG. 17A is a schematic illustration of a conventional optical displaysystem.

FIG. 17B is a schematic illustration of an optical display according toan embodiment.

DETAILED DESCRIPTION

The present inventors realized that prior art backlight solutions whichutilize LED light sources and which are intended for uniformillumination applications, such as transmissive and reflective displaysand thin profile panel luminaires suffer from degraded overall opticalsystem efficiency due to one or more of the following limitations:

-   -   1. The inherent optical loss originating from the absorptive        loss that stems from the package housing the LED emitters;    -   2. The etendue of the coupling optics among the LED emitters,        LED package and the light guide plate;    -   3. The assembly tolerances in five degrees of freedom        originating from the placement of the LED package, the air gap        between the package and the light guide plate and the alignment        of light guide plate to the LED package; and    -   4. The continuing desire to reduce the overall thickness of the        backlighting units' thickness.        The quest for slimmer light panels and thinner display,        particularly in the mobile digital appliance markets,        exacerbates the aforementioned challenges.

Embodiments are drawn to a light emitting device which includes a lightemitting diode (LED) assembly with a support having an interstice and atleast one LED located in the interstice and a transparent materialencapsulating the at least one LED and which forms at least part of anoptical launch and/or a waveguide. In other words, the LED dieencapsulant forms the optical launch and/or the waveguide, such as alight guiding plate. Other embodiments are drawn to an integrated backlight unit which includes the optical launch and a back light waveguideoptically coupled to the optical launch. Preferably, the back lightwaveguide directly contacts the transparent material. Other embodimentsare drawn to methods of making light emitting devices and integratedback light units. Embodiments of the method of making an integrated backlight unit include making a light emitting device by attaching at leastone LED in an interstice located in a support and encapsulating the atleast one LED with a transparent material which forms at least part ofan optical launch and/or a waveguide. In one embodiment, the method ofmaking an integrated back light unit also includes optically coupling aback light waveguide to the optical launch. Preferably, the back lightwaveguide directly contacts the transparent material.

This integrated back light unit architecture eliminates the first-levelpackaging of LED emitters and allows very efficient optical launch ofemitted photons into the waveguide, such as a light guide plate withoutthe in-package and coupling losses associated with conventionalarchitectures of back light units for display and illuminationapplications. This provides the direct coupling of the light guide plateto the LED emitters by co-molding that eliminates or reduces undesirableoptical interfaces.

FIGS. 1 and 2 are schematic illustrations of an a packaged LED deviceunit 100 in which the LED die encapsulant forms the optical launch andwhich can be used with a waveguide to form an integrated back lightunit, according to alternative embodiments. The unit 100 includes asupport, such as a molded lead frame 108 (as shown in FIG. 1) or acircuit board 114 (as shown in FIG. 2) supporting at least one LED die112 (e.g., chip) in an interstice 132, a transparent material 117encapsulating the at least one LED die 112 and which forms at least partof an optical launch 102, and a plurality of leads/contacts 130 (one ofwhich is shown in FIG. 1). The interstice 132 may comprise any suitableintervening space between the bottom and side surface(s) of the packagethat contains the LED die 112. The interstice 132 may have a slit shapeor any other shape, such as cylindrical, conical, polyhedron, pyramidal,irregular, etc. The LED die 112 may include one or more light-emittingsemiconductor elements (such as red, green and blue emitting LEDs orblue emitting LEDs covered with yellow emitting phosphor) which may bemounted on an upper surface of a lead/contact 130.

As shown in FIGS. 3D and 4B, the support, such a lead frame 108 or aprinted circuit board 114 and at least one LED die 112 located in theinterstice 132 in the support together form a light emitting diode (LED)assembly 113 of the packaged LED unit 100. As shown in FIGS. 4A and 4C,the lead frame 108 of the assembly 113 may comprise a molded lead framewhich includes an open top, molded polymer housing 116 with embeddedplural (e.g., at least first and second) electrically conductive leadframe 108 leads 130. The interstice 132 is located between sidewalls anda bottom surface of the housing 116 and the at least one LED (e.g., LEDdie) 112 is located in the interstice 132 and electrically connected tothe first and to the second electrically conductive lead frame leads130.

The LED die 112 may be mounted to the upper surface the lead/contact 130using any suitable bonding or attaching technique. In embodiments, thesurface of the LED die 112 may be electrically insulated from thelead/contact 130 via an insulating material (e.g., a sapphire layer),which may be or may form part of the support substrate of the die 112.

As illustrated in FIGS. 3C and 4C, the LED die 112 may be wire bondedwith wire bonds 124 to the first and to the second electricallyconductive contacts/leads, such as lead frame leads 130. Thus, theactive region of the LED die 112 may be electrically connected to thefirst lead 130 by a first wire 124, which may be bonded to a first bondpad region of the die 112 as illustrated in FIG. 3C. A second wire 124may be bonded to a second bond pad region of the die 112 to electricallyconnect the die 112 to the second lead 130. In an alternativeembodiment, the at least one LED die 112 is bonded to the electricallyconductive lead frame leads 130 as illustrated in FIG. 4A. Preferably,all electrical connections (e.g., the wire bonds 124 or direct bonds)between the LED die 112 and the contacts/leads 130, such as the firstand the second electrically conductive lead frame leads 130 are locatedwithin the transparent material of the optical launch 102.

In the embodiment illustrated in FIG. 2, the packaged LED unit 100 isformed on a circuit board 114 support, such as a printed or flexiblecircuit board rather than on a molded lead frame. The unit 100 of FIG. 2also includes a housing 116, which may be a protective, open top packagearound the die 112 and leads 130. In embodiments, the housing 116 may bea molded epoxy material, although other materials (e.g., ceramic,plastic, glass, etc.) may be utilized. The leads 130 may be at leastpartially embedded in the housing 116. As shown in FIG. 2, the housing116 may form the sidewalls and optionally at least a portion of thebottom surface of the unit 100 and may include an opening 111 in itsupper surface exposing at least one LED die 112. In the embodiment ofFIG. 2, a printed circuit board 114 forms at least part of the bottomsurface of the unit 100. In embodiments, the housing 116 forms a pocketwith an interstice 132 that surrounds the LED die 112.

Preferably, the interstice 132 may be filled with an encapsulantmaterial 117 that is optically transparent (e.g. at least 80%, such as80-95% transmissive) over at least a selected wavelength range, such as400-700 nm. The transparent material 117 may be silicone, acrylicpolymer (e.g., poly(methyl methacrylate) (“PMMA”) or epoxy or any othersuitable transparent material, and forms at least a portion of theoptical launch 102. Optionally, the encapsulant may include a phosphoror dye material mixed in with the silicone, polymer or epoxy. In anembodiment, the housing 116 includes a single LED die 112. In otherembodiments, multiple LED die 112 may be included within a housing 116,either in the same or in different interstice 132 of the housing 116, asdiscussed in more detail below.

In an embodiment illustrated in FIGS. 1, 3D, 4B, 4D and 4H, thetransparent material overfills the interstice 132 and extends from theinterstice 132 above an upper surface of the support 108/114 (i.e.,above the upper surface of the housing/package 116 or assembly LED 113).In this embodiment, a bottom portion of a waveguide 104 contacts thetransparent material of the launch 102 above the interstice 132. Thewaveguide 104 is attached to the optical launch 102 by at least one of aclamp and a tape (136 and/or 138) above the interstice 132 to form theintegrated back light unit 300, as shown in FIGS. 4D and 4H. Preferablya reflective material 110, such as a silver or aluminum layer or anotherreflective material is located over at least a portion of side surfacesof the transparent material of the optical launch 102 which extendsabove the upper surface of the LED assembly 113, as shown in FIGS. 3Dand 4B.

In another embodiment shown in FIG. 5C, the transparent material 117 ofthe optical launch 102 only partially fills the interstice 132. In thisembodiment, a bottom portion of the waveguide 104, such as a light guidepanel, extends into the interstice 132 to contact the transparentmaterial of the launch 102 in the interstice 132, as shown in FIG. 5C.The light guide panel 104 is attached to the optical launch 102 bysidewalls of the support structure (e.g., the housing/package 116)surrounding the interstice 132. In one non-limiting configuration ofthis embodiment that will be described in more detail below, the package116 may comprise a molded or stamped pocket 146 located on a circuitboard 114.

In another embodiment shown in FIG. 5D, the optical launch 102 isomitted and the transparent material molding material forms a waveguide104, such as a light guiding plate. The molding material in the form ofthe light guiding plate 104 completely fills the interstice 132 andextends out of the interstice 132 over the upper surface of the support,such as a molded lead frame.

In one embodiment, the LED die 112 may be a white light emitting LED(e.g. a blue LED 112B covered with a yellow emitting phosphor whichtogether appear to emit white light to an observer) or plural closelyspaced LED die (e.g. plural red, green, blue emitting LED die 112R,112G, 112B), as shown in FIG. 3C.

Any suitable LED structure may be utilized. In embodiments, the LED maybe a nanowire-based LED. Nanowire LEDs are typically based on one ormore pn- or pin-junctions. Each nanowire may comprise a firstconductivity type (e.g., doped n-type) nanowire core and an enclosingsecond conductivity type (e.g., doped p-type) shell for forming a pn orpin junction that in operation provides an active region for lightgeneration. An intermediate active region between the core and shell maycomprise a single intrinsic or lightly doped (e.g., doping level below10¹⁶ cm⁻³) semiconductor layer or one or more quantum wells, such as3-10 quantum wells comprising a plurality of semiconductor layers ofdifferent band gaps. Nanowires are typically arranged in arrayscomprising hundreds, thousands, tens of thousands, or more, of nanowiresside by side on the supporting substrate to form the LED structure. Thenanowires may comprise a variety of semiconductor materials, such asIII-V semiconductors and/or III-nitride semiconductors, and suitablematerials include, without limitation GaAs, InAs, Ge, ZnO, InN, GaInN,GaN, AlGaInN, BN, InP, InAsP, GaInP, InGaP:Si, InGaP:Zn, GaInAs, AlInP,GaAlInP, GaAlInAsP, GaInSb, InSb, AlN, GaP and Si. The supportingsubstrate may include, without limitation, III-V or II-VIsemiconductors, Si, Ge, Al₃O₃, SiC, Quartz and glass. Further detailsregarding nanowire LEDs and methods of fabrication are discussed, forexample, in U.S. Pat. Nos. 7,396,696, 7,335,908 and 7,829,443, PCTPublication Nos. WO2010014032, WO2008048704 and WO2007102781, and inSwedish patent application SE 1050700-2, all of which are incorporatedby reference in their entirety herein.

Alternatively, bulk (i.e., planar layer type) LEDs may be used insteadof or in addition to the nanowire LEDs. Furthermore, while inorganicsemiconductor nanowire or bulk light emitting diodes are preferred, anyother light emitting devices may be used instead, such as laser, organiclight emitting diode (OLED) (including small molecule, polymer and/orphosphorescent based OLED), light emitting electrochemical cell (LEC),chemoluminescent, fluorescent, cathodoluminescent, electron stimulatedluminescent (ESL), resistive filament incandescent, halogenincandescent, and/or gas discharge light emitting device. The lightemitting device may emit any suitable radiation wavelength (e.g., peakor band), such as visible radiation (i.e., visible light having any oneor more peak or band wavelengths in a range of 400 to 700 nm).

In one embodiment illustrated in more detail in FIG. 4A, the unit 100includes a red LED n contact 130RN, a red LED p contact 130RP, a greenLED n contact 130GN, a LED green p contact 130GP, a blue LED n contact130BN and blue LED p contact 130BP. Each lead/contact 130 may be formedof an electrically conductive material (e.g., a metal, such as copper,which may be optionally coated with nickel and/or silver). Theleads/contacts 130 may be formed as part of a lead frame, packaged andseparated from the frame to produce individual units 100. Theleads/contacts 130 may extend generally parallel without contacting oneanother between a first side surface 101 and a second side surface 103of the unit 100.

The unit 100 is not limited to three LED die 112. Embodiment units 100include a housing/package 116 that may include dozens or hundreds ormore LED die 112R, 112G, 112B. The packaged LED unit 100 may include aplurality of leads/contacts 130RN, 130RP, 130GN, 130GP, 130BN, 130BP toelectrically connect the LED die 112R, 112G, 112B, as illustrated inFIG. 4A. Each of the die 112R, 112G, 112B may be mounted on a topsurface of a lead and electrically connected to at least two differentleads, as described above.

The unit 100 together with the waveguide 104 may be mounted to a supportsurface 200, such as a base plate 200, in either a top-emittingconfiguration (e.g., with the light emitted perpendicular to the majorsurface 202 of the plate 200 supporting the unit 100) or in aside-emitting configuration (e.g., with the light emitted parallel tothe major surface 202 of the plate 200 supporting the unit 100), asillustrated in FIGS. 4D and 4G. For example, the integrated back lightunit 300 may be located over a base plate 200 in a side emittingconfiguration such that a side of the packaged LED device unit 100support, e.g., molded lead frame 108/116, is located on a major surfaceof the base plate 200, and the exposed contacts 130 on the side of thepackage 116 of the molded lead frame 108 contact the respectiveelectrodes on the base plate 200. In this embodiment, at least one of adiffuser 144, filter 142 and polarizer 140 film(s) are located overfirst and second surfaces of the waveguide 104 as illustrated in FIGS.4D, 4E, 4F and 4H.

Embodiments also include methods of making a light emitting device. Anembodiment includes providing a light emitting diode (LED) assembly 113which includes a support, such as molded lead frame 108 or a circuitboard 114, having an interstice 132 and at least one LED die 112 locatedin the interstice 132. The method also includes encapsulating the atleast one LED die 112 with a transparent material 117 which forms anoptical launch 102 which at least partially fills the interstice 132.

In one embodiment illustrated in FIGS. 3A-D, 4A-H and 5A-5C, the supportcomprises the molded lead frame 108. The molded lead frame 108 is formedby molding a polymer housing 116 around a lead frame to embed first andsecond electrically conductive lead frame leads 130 in the housing 116.The molded lead frame 108 includes a housing 116 (e.g., molded packageportion) with the interstice (e.g., alignment channel or cavity) 132located between sidewalls and a bottom surface of the housing 116, asshown in FIGS. 5A and 5B.

If needed, an electrode material is formed in the interstice 132, suchas by coating the leads 130 with a Ni and/or Ag layer. The reflective110 material is then formed on sidewalls of the support (e.g., housing116) surrounding the interstice 132 prior to encapsulating the LED die112, as shown in FIG. 5B. The die bond pads are then formed by laserablation or chemical etching of the exposed leads 130, if the leads donot have the required bond pad shape.

The at least one LED die 112 is placed in the interstice 116, as shownin FIG. 5B, and electrically connected to the first and to the secondelectrically conductive lead frame leads 130. In an embodiment, the atleast one LED die 112 is wire bonded to the first and to the secondelectrically conductive lead frame leads 130, as shown in FIG. 4C.

Additionally, the step of encapsulating the at least one LED die 112with the transparent material 117 includes encapsulating the wire bonds124 between the at least one LED die 112 and the first and the secondelectrically conductive lead frame leads 130, such that the wire bondsare located within the transparent material of the optical launch 102,as shown in FIG. 5C.

The method further includes optically coupling a back light waveguide104 to the optical launch 102, such that the back light waveguide 104directly contacts the transparent material. In an embodiment, the backlight waveguide 104 is a light guide panel and the transparent materialof the launch 102 only partially fills the interstice 132 (e.g., 25-75%fill, such as about 50% fill), as shown in FIG. 5C. In this embodiment,the step of optically coupling the back light waveguide 104 includesinserting a bottom portion of the light guide panel 104 into theinterstice 132 to contact the transparent material of the launch 102 inthe interstice 132, such that the light guide panel 104 is attached tothe optical launch 102 by sidewalls of the support structure (e.g.,molded housing 116) surrounding the interstice 132, as shown in FIG. 5C.

In another embodiment shown in FIG. 5D, the optical launch 102 isomitted and the transparent material molding material forms a waveguide104, such as a light guiding plate. The molding material is solidifiedin the form of the light guiding plate 104 which completely fills theinterstice 132 and extends out of the interstice 132 over the uppersurface of the support, such as a molded lead frame 108. Thus, thewaveguide 104 is made of a moldable polymer material, directly contactsthe upper surface of the LED die 112, and acts as the encapsulant forthe LED die 112.

In a method of alternative embodiments illustrated in FIGS. 6A-6D and7A-7D, the support is a circuit board 114. A pocket 146 containing theinterstice 132 is located on the circuit board 114. The pocket 146 maybe a molded structure, such as a housing 116, located on a surface ofthe circuit board 114. In this embodiment, the interstice 132 is locatedbetween sidewalls and a bottom surface of the molded structure 116. TheLED die 112 is placed in the interstice 132 and wire bonded to contactpads 130 on the surface of the circuit board 114. Preferably, the stepof encapsulating the at least one LED die 112 with the transparentmaterial of the optical launch 102 comprises encapsulating the wirebonds 124 such that the wire bonds 124 are located within thetransparent material 117 of the optical launch 102.

As illustrated in FIGS. 6A-6D, the molded structure 116 having aninterstice 132 may be molded (i.e., formed) directly on the circuitboard 114. In this method, a circuit board 114, such as a printedcircuit board or a flexible circuit board with die bond pads and otherelectrodes is provided, as shown in FIG. 6A.

Then, an epoxy or another suitable molding material is provided to thesurface of the board 114 and molded to form the pocket 146 (e.g., themolded housing structure 116). Preferably, a reflective white epoxy orsilicone die bond dam material, such as a methyl rubber RTV siliconematerial sold under the names KER-2020-DAM or KER-2000-DAM by Shin-Etsu,is used to form the structure 116, as shown in FIG. 6B.

In an alternative embodiment, the pocket 146 comprises a moldedstructure 116 which is attached to the surface of the circuit board 114after being molded separately from the circuit board 114, rather thanbeing molded on the surface of the circuit board 114. This moldedstructure 116 may comprise a molded lead frame (e.g., a metal patternsof contacts on an insulator, such as a polymer or ceramic, that formsinterconnects as base and connections for LED die) or an insulatingpocket. Alternatively, the pocket 146 may comprise a stamped housingstructure 116, such as a reflecting, waveguiding pocket, which isstamped on the circuit board 114. For example, the stamped pocket 146may comprise an acrylic glass (e.g., PMMA) pocket coated with areflective layer 110, such as an aluminum layer. The molded or stampedstructure 116 may be attached to the circuit board 114 using anysuitable adhesive, such as UV curable epoxy.

After forming the molded or stamped structure 116, one or more LED die112 may located (e.g., attached) in the interstice 132 and connected(e.g., wire bonded) to the bond pads on the circuit board 114, as shownin FIG. 6C. If the structure 116 is a molded lead frame, then the LEDdie may be bonded inside the lead frame.

Next, the optical launch 102 may be formed in the interstice 132 byencapsulating the LED die 112 in epoxy, acrylic polymer or silicone.After forming the optical launch 102, the waveguide (e.g., light guidepanel) 104 may be located in the remaining, unfilled upper part of theinterstice 132 in the structure 116, as shown in FIG. 6D. The step ofoptically coupling the back light waveguide 104 to the optical launchmay comprise inserting a bottom portion of the waveguide (e.g., lightguide panel) 104 into the interstice 132 to contact the transparentmaterial of the launch 102 in the interstice, such that the light guidepanel is attached to the optical launch by sidewalls of the support(e.g., structure or housing) 116 surrounding the interstice 132.

In an alternative method, one or more LED die 112 are first located onthe surface of the circuit board 114 and then the structure 116 isformed around the LED die 112 (e.g., molded, stamped or attached aroundthe LED die).

In an alternative embodiment shown in FIG. 6E, the optical launch 102 isomitted and the transparent material molding material forms a waveguide104, such as a light guiding plate. The molding material in the form ofthe light guiding plate 104 completely fills the interstice 132 andextends out of the interstice 132 over the upper surface of thestructure 116.

In another embodiment illustrated in FIGS. 7A-7D, the circuit board 114comprises a bent flexible circuit board 114 having a first portion 114 aand a second portion 114 b extending in a non-parallel direction withrespect to the first portion 114 a. For example, the second portion 114b may extend 20-160 degrees, such as 80-100 degrees, e.g., perpendicularwith respect to the first portion 114 a, as shown in FIG. 7A.

The pocket 146 includes a structure 116 which is molded, attached orstamped around the bent flexible circuit board 114. The structure 116may comprise the white reflective epoxy or the reflecting, waveguiding,acrylic glass pocket described above. The first portion 114 a is exposedin the interstice 132 on a bottom surface of the pocket 146, and thesecond portion 114 b extends through the bottom surface of the pocket146 in the non-parallel direction with respect to the first portion 114a, as shown in FIG. 7B.

The method then proceeds similar to the steps shown in FIGS. 6C-6D,where the at least one LED die 112 is attached to the first portion 114a of the bent flexible circuit board in the interstice 132 in the pocket146, as shown in FIG. 7C. The LED die 112 is then encapsulated with thetransparent material of the optical launch 102 and the waveguide (e.g.,light guide panel) 104 may be located in the remaining interstice 132 inthe structure 116, as shown in FIG. 7D.

In an alternative embodiment shown in FIG. 7E, the optical launch 102 isomitted and the transparent material molding material forms a waveguide104, such as a light guiding plate. The molding material in the form ofthe light guiding plate 104 completely fills the interstice 132 andextends out of the interstice 132 over the upper surface of thestructure 116.

In another alternative embodiment, the transparent material 117 of theoptical launch 102 and/or the light guiding plate is formed toencapsulate the LED die 112 such that overfills the interstice 132 andextends from the interstice 132 above an upper surface of the support108/116 which forms the sidewall(s) of the interstice 132. In thismethod, the step of optically coupling the back light waveguide 104includes contacting a bottom portion of the waveguide 104 to thetransparent material of the optical launch 102 above the interstice 132and attaching the waveguide 104 to the optical launch 102 by at leastone of a clamp and a tape (136 and/or 138) above the interstice 132, asshown in FIG. 4H, for example. Alternatively, the waveguide (e.g., anactive light guiding plate) 104 may be attached to the optical launch102 by an optically transparent molding material (e.g., polymer orepoxy) 106 which is formed by injection molding or casting around theinterface of the waveguide 104 and the optical launch 102. The opticallytransparent molding material 106 preferably has the same or similar(e.g., differs by less than 10%) index of refraction as the index ofrefraction of the waveguide 104. In one embodiment, the method furtherincludes a step of forming a reflective material 110 over side portionsof the transparent material of the optical launch 102 extending abovethe upper surface of the support, as shown in FIGS. 3D and 4B, forexample.

In another embodiment, the method further includes forming at least oneof a diffuser 144, filter 142 and polarizer 140 film(s) over first andsecond surfaces of the waveguide 104, as shown in FIG. 4H. The methodfurther includes mounting the unit 100 connected to the waveguide 104over a base plate 200 in a side emitting configuration such that a sideof the support 108/116 is located on a major surface 202 of the baseplate 200, as shown in FIG. 4H. The waveguide 104 may be attached to theunit 100 before or after attaching the unit 100 to the base plate 200.

FIG. 8 illustrates a circuit diagram illustrating a circuitconfiguration that allows individual control of LED die 112G, 112R, 112Bin an array of LED die 112. When using LEDs of different color, such asred, green and blue, separate buses 126G, 126B, 126R are provided foreach color LED die. Two buses 126, a positive bus and a negative bus,are typically provided for each color emitting LED die. LED die 112which emit the same color light may be wired in series such that a firstlead of the first LED die 112 in the array of series connected LED die112 is electrically connected to one bus, such as the positive or thenegative bus, and a second lead of the last LED die 112 in the arrayelectrically connected to the other bus of the two buses.

FIG. 9 is a ray diagram illustrating the effect of misalignment of theoptical launch 102 of an integrated back light unit 100 and the backlight waveguide 104. Lead line 118 illustrates a Y-axis misalignment.Lead line 120 illustrates a Y position misalignment. Lead line 122illustrates the molding foot height. Five thousand simulations were runand a Monte Carlo analysis performed on the simulations. The results ofthe Monte Carlo analysis are illustrated in FIG. 10 which is a plot ofdistribution as a function of coupling efficiency, showing an acceptabledevice performance even with the misalignment.

It should be noted that the LED may be attached to the support using anysuitable method in the embodiments described and illustrated above. Forexample, the LED may be attached using die attachment, flip chipattachment (e.g., flip chip bonding) or grafting methods. The LED may beattached to the support in a coplanar configuration (e.g., the majorsurface of the LED chip is located on and extends parallel to the majorsurface of the support on which the LED is located) or an edge mountconfiguration (e.g., the minor edge surface of the LED chip is locatedon and extends parallel to the major surface of the support on which theLED is located). The support may comprise any suitable material, such aspolymer or epoxy housing or circuit board, metal leads encapsulated inthe polymer or epoxy housing (e.g., molded lead frame), a metal support,a semiconductor (e.g., III-nitride or Group IV, such as silicon)support, etc. The electrical contact may be made to the LED using anysuitable contacting method, such as wire bonding, flip chip bonding, andsurface mount diode contacts (e.g., contacting a bottom surface of thediode).

While the optical launch is described and illustrated as being attachedto one edge of the light guiding plate, alternative configurations mayalso be used, such as attaching the optical launch to a major surface(e.g., face) of the light guiding plate. Alternatively, plural opticallaunches may be directly attached to plural (e.g., 2, 3 or 4) edgesand/or faces of the light guiding plate. Furthermore, a single launch(e.g., an L-shaped, U-shaped or rectangular shaped) launch may bedirectly attached to plural edges and/or faces of the light guidingplate. The device (e.g., back light unit) may be used in any suitablesystem, such as a system used for illumination (e.g., a lighting deviceor lamp) or display (e.g., liquid crystal display).

In summary, molding an optically transparent material, such as siliconeor acrylic (poly(methyl methacrylate)) with a reflector on the sidesurfaces over a straight row of RGB LED die forms an optical launch thatmates directly to the backlight waveguide. This configuration results inone or more of the following non-limiting advantages, such as improvedoptical coupling, reduced power consumption, shorter mixing length,smaller overall package size, and reduced cost because there is no needfor individual packages. Specifically, molding the RGB LED die directlyinto the optical launch improves optical coupling, such as by directlybutt coupling the optical launch to the waveguide. This allows a row ofRGB LED die to be aligned along the edge of a waveguide and to launchlight directly down the core of the waveguide through the opticallaunch. The optical launch shape improves coupling and shortens themixing length, and allows metallizing the sides of the optical launchwith a reflective metal layer to form the optical launch. The opticallaunch may be easily connected to the waveguide using any suitablemethod, such as clamping, taping, molding or inserting a panel shapedwaveguide into an interstice partially filled with the optical launchmaterial. The device is scalable in width, length and thickness.

This configuration further results in one or more of the followingadditional non-limiting advantages:

-   -   1. LED-emitted photons “see” an uninterrupted optical path into        the light guide;    -   2. There is no discontinuity in the index of the photons flight        path, thereby eliminating or reducing Fresnel loss;    -   3. Photons that are launched at incident angles larger than the        light guide's (e.g., launch and/or waveguide) total internal        reflection are guided back by reflective surfaces;    -   4. The optical loss due to the LED package is reduced or        eliminated;    -   5. The total internal reflection angle of LED emitter “seeing”        the light guide plate is increased to 42 degrees instead of the        26 degree angle for LED emitter to air. This enables a much        larger fraction of the emitting photons to be launched into the        light guide plate.    -   6. The co-molding of the light guide plate with the LED assembly        eliminates one level of critical alignment. This results in        improved coupling efficiency as well as narrow manufacturing        distribution.    -   7. The co-molded light guide plate, owing to the elimination of        the first-level LED package, allows much thinner back light unit        thickness.

Alternative embodiments of the invention also provide the followingoptional, non-limiting advantages. The selected LED emitters may berandomly distributed within the back light unit. The wavelengths of theLED emitters are not limited to red, green and blue. A much denserplacement of LED emitters within the back light unit becomes possible.Owing to the compact and area efficient architecture, it is possible toconstruct a large back light unit panel that is composed of multiple,smaller-sized back light unit that are arranged in grid geometry. Theco-molded optical launch and light guide are readily realized on anysuitable electrical substrate, organic or inorganic.

FIGS. 11A-11B illustrate alternative embodiments of integrated backlight units 100. In the embodiment illustrated in FIG. 11A, adye/phosphor layer 302 with embedded dye and/or phosphor particles 304is located at the distal end of the back light waveguide 104. In anaspect, the dye and/or phosphor particles 304 down convert the lightfrom the LED 112. That is, the dye and/or phosphor particles 304 absorblight emitted at a first wavelength from the LED 112 and re-emit thelight at a second, longer wavelength. For example, if the LED 112 emitsblue light, dye and/or phosphor particles 304 may be selected such thatthe dye/phosphor layer 302 emits yellow, green or red light. In anotheraspect, multiple different types of dye and/or phosphor particles 304may be embedded in the dye/phosphor layer 302 such that more than onedifferent color light is emitted from the dye and/or phosphor particles304. In an aspect, the different colors of light may combine in thedye/phosphor layer 302 such as to form white light. For example, forblue light emitting LEDs, particles 304 may comprise YAG:Cenanoparticles which emit yellow light. For material and wavelengthcombinations may be used. Preferably, the dye and/or phosphor particles304 are nanoscale particles, such as quantum dots.

In the embodiment illustrated in FIG. 11B, the dye and/or phosphorparticles 304 are embedded directly in the back light waveguide 104. Inan embodiment, the back light waveguide 104 is made of an opticallytransparent polymer material. Preferably, as in the previous embodiment,the dye and/or phosphor particles 304 are nanoscale particles, such asquantum dots. In another embodiment, the dye and/or phosphor particles304 may be embedded in the optical launch, between the optical launchand the waveguide and/or in both the optical launch and the waveguide.

FIG. 12 is a schematic illustration of a side cross sectional view of anintegrated back light unit 100 according to another embodiment. In thisembodiment, the integrated back light unit 100 includes an opticallaunch 102 and a waveguide 104. This embodiment also includes an indexmatching compound 117A in the gap between the optical launch 102 and thewaveguide 104 to improve the efficiency of the passage of photons 105from the optical launch 102 into the waveguide 104. Optionally, areflective material 110 as discussed above may be provided extendingacross the gap between the optical launch 102 and the waveguide 104. Thereflective material acts as a mechanical joint between the launch andthe waveguide and confines photons which would have escaped otherwise tothe waveguide. Preferably, the mechanical joint comprises a metal stripof reflective material (e.g., Al, Ag, etc.) which is wrapped around aninterface between the optical launch and the waveguide.

FIG. 13A is a schematic illustration of a side cross sectional view ofan integrated back light unit 100 illustrating the location of a hotspot 119 in brightness in the waveguide 104. The inventors havediscovered that the light provided from the optical launch 102 to thewaveguide 104 may not be homogeneous, resulting in a hot spot 119 inbrightness in the waveguide 104. To help prevent light from escaping thewaveguide 104, a circumferential polarizer 140 may be provided aroundthe waveguide 104 as illustrated in FIG. 13B. With the polarizer 140,only a fraction of the light in the hot spot 119 escapes the waveguide104 while most of the light is directed back into the waveguide 104 bythe polarizer 140. That is, the circumferential polarizer is locatedaround the waveguide 104 to reduce light loss from the optical hot spotin the back light waveguide 104. The hot spot 119 band brightnessdecreases leading to an increase in brightness of the entire unit 100.Furthermore, the high angle photon loss is decreased significantly, suchas by 30 to 50%. If desired, the mechanical joint metal strip 110 and/orthe index matching compound 117A shown in FIG. 12 may also be used incombination with the circumferential polarizer 140 shown in FIG. 13B.

FIGS. 14A and 14B are schematic illustrations of alternative embodimentsof integrated back light units with embedded dye and/or phosphorparticles 304. These embodiments are similar to the embodimentsillustrated in FIGS. 11A and 11B discussed above. In the embodimentillustrate in FIG. 14A, the embedded dye and/or phosphor particles 304are located only in the optical launch 102. In the embodimentillustrated in FIG. 14B, the embedded dye and/or phosphor particles 304are located only in the waveguide 104. As illustrated in FIG. 11B, theembedded dye and/or phosphor particles 304 may be located in both theoptical launch 102 and the waveguide 104.

FIGS. 15A and 15B are schematic illustrations of embodiments ofintegrated back light units 400A, 400B with wavelength convertingmaterials, such as embedded dye and/or phosphor particles 304. In theembodiment of the integrated back light unit 400A illustrated in FIG.15A, the dye and/or phosphor particles 304 are distributed throughoutthe optical launch 102, the waveguide 104 or both such that light fromall of the LEDs 112 travels to the dye and/or phosphor particles 304. Inthe embodiment of the integrated back light unit 400B illustrated inFIG. 15B, the dye and/or phosphor particles 304 are distributed in theoptical launch 102, the waveguide 104 or both such that light fromselected LEDs 112 travels to the dye and/or phosphor particles 304. Forexample, the dye and/or phosphor particles 304 may be configured suchthat only light from the red LEDs 112R travels to the dye and/orphosphor particles 304. Alternatively, the dye and/or phosphor particles304 may configured such that only light from the blue LEDs 112B or thegreen LEDs 112G or any combination of red, blue and or green LEDs 112R,112B, 112G travels to the dye and/or phosphor particles 304.

FIG. 16 is a schematic illustration of a method of making integratedback light units 100 according to an embodiment. In the methodillustrated in FIG. 16, multiple rows 109A, 109B of LEDs 112 are firstmounted (e.g., die attached and wire bonded or flip chip attached) on asupport, such as an organic or inorganic substrate or panel, or asemiconductor wafer 107. Any of the methods illustrated in FIGS. 5A to7E may then be used to fabricate a “panel” of integrated back lightunits 100. After fabricating the “panel” of integrated back light units100, the panel or wafer 107 may be separated into rows of LEDs 112(e.g., diced by saw cutting, etc.) to form individual integrated backlight units 100, each having a one or more rows of LEDs. The units 100may be encapsulated with the optical launch 102 and/or the waveguide 104before or after the separation into rows. Preferably, the all of theLEDs 112 on the support are gang molded with the launch and/or waveguidebefore the separation. If desired, all LEDs 112 on the panel or wafermay be performance tested before the separation. Alternatively, each rowmay be performance tested separately (i.e., testing each row of LEDs atone time) before the separation and then separated and used in a backlight unit 100 if it passes the test or discarded if it fails the test.

FIGS. 17A and 17B illustrate a conventional optical display system andan optical display system 500 according to an embodiment, respectively.The conventional optical display system shown in FIG. 17A includes adisplay 502 that includes an array of pixels 504 located in a housing503. The array of pixels 504 create the images that are displayed. Theconventional optical display system further includes either micromirrorsused in digital light processing (DLP) or twisted nematic polymers usedin liquid crystal (LC) displays. To illuminate the array of pixels 504,the conventional display system includes separate red, green and bluelight sources 506R, 506G, 506B, such as lamps, which are remotelylocated from the array of pixels 504. Light from the separate red, greenand blue light sources 506R, 506G, 506B is reflected off the arraypixels 504. The reflected light 508 can be viewed by an observer.

The optical system 500 shown in FIG. 17B according to an embodiment ofthe invention includes an integrated back light unit 100 opticallyconnected to a first face 510A of a polarizer 510. The system alsoincludes a display 502 which includes a housing an array of pixels 504optically connected to a second face 510B of the polarizer 510. In anembodiment, the first face 510A of the polarizer 510 and the second face510B of the polarizer 510 are not parallel with each other. However, thepolarizer 510 is configured to direct light from the integrated backlight unit 100 to the display 502 as indicated by the arrows 505. In anembodiment of the optical system 500, the first face 510A and the secondface 510B are at an approximately 90° angle. Thus, in this embodiment,integrated back light unit 100 may be optically attached to a verticalface of the polarizer 510 and the optical display 502 may be opticallyattached to a horizontal face of the polarizer 510. Further, with theuse of a single polarizer 510 to direct the source light from theintegrated back light unit 100 to the display 502, the complex optics ofthe mirrors of DLP and the twisted polymers LC are not needed.

The system may comprise any suitable image projection system which canproject an image, such as a color image on a surface (e.g., on a surfaceof a screen or on a surface of another object, such as window or visor)or in a space between surfaces. Examples of image projection systemsinclude projectors, wearable displays, pico displays and head updisplays. A head up display (“HUD”) is a display of instrument readingsin an aircraft or a vehicle that can be seen without lowering the eyes,typically through being projected onto a windshield or a visor.

A method of projecting an image 508 from the system 500 includesproviding plural colors of light 505, such as red, green and blue peakwavelength light or another combination of light colors from theintegrated back light unit 100 to the first face 510 a of the polarizer510. The method also includes providing the light 505 from the secondface 510 b of the polarizer 510 to an array of pixels 504 of a display502. The pixels 504 convert the light to an image and project the image508 from the array of pixels 504 through the polarizer 510 onto asurface or into a space between surfaces.

The integrated back light unit 100 used in the optical system 500 mayinclude any of the integrated back light units 100 described above orany other suitable multi-color LED light sources. The integrated backlight unit 100 may include an optical launch 102 with a plurality ofLEDs 112 optically attached to a waveguide 104. Preferably, theplurality of LEDs include red, green and blue LEDs 112R, 112G, 112B.

Preferably, the integrated back light unit 100 provides uniformillumination across the array of pixels 504. In an embodiment, theillumination varies by less than 5% across the array pixels.

Although the foregoing refers to particular preferred embodiments, itwill be understood that the invention is not so limited. It will occurto those of ordinary skill in the art that various modifications may bemade to the disclosed embodiments and that such modifications areintended to be within the scope of the invention. All of thepublications, patent applications and patents cited herein areincorporated herein by reference in their entirety.

What is claimed is:
 1. An optical display system comprising: apolarizer; an integrated back light unit optically connected to a firstface of the polarizer, wherein the integrated back light unit comprisesat least one light emitting diode mounted on a support in aside-emitting configuration that provides illumination to a front sideof the support, wherein the at least one light emitting diode is locatedon, and extends parallel to, a major surface of the support, and emitslight parallel to the major surface of the support, and the integratedback light unit further comprises a waveguide that directs light fromthe at least one light emitting diode toward the front side of thesupport and to the first face of the polarizer; and a display comprisingan array of pixels optically connected to a second face of thepolarizer, wherein the first face of the polarizer and the second faceof the polarizer are not parallel; and wherein the polarizer isconfigured to direct light from the integrated back light unit to thedisplay.
 2. The system of claim 1, wherein the integrated back lightunit comprises an optical launch, and the waveguide is opticallyconnected to the optical launch and the waveguide is located adjacentthe polarizer.
 3. The system of claim 1, wherein the first face and thesecond face make an approximately 90° angle.
 4. The system of claim 1,wherein the integrated back light unit comprises a plurality of red,blue and green light emitting diodes.
 5. The system of claim 1, whereinthe integrated back light unit provides uniform illumination across thearray of pixels.
 6. The system of claim 1, wherein the illuminationvaries by less than 5% across the pixels and wherein the waveguidecomprises particles of a wavelength converting material embedded withinan optically transparent material.
 7. The system of claim 1, wherein thearray of pixels comprises an array of liquid crystal or DLP mirrorpixels.
 8. The system of claim 1, wherein the display comprises an imageprojection display.
 9. The system of claim 8, wherein the imageprojection display comprises a wearable display, a pico display or ahead up display.
 10. A method of making an optical display systemcomprising: optically connecting integrated back light unit to a firstface of a polarizer, wherein the integrated back light unit comprises atleast one light emitting diode mounted on a support in a side-emittingconfiguration that provides illumination to a front side of the support,wherein the at least one light emitting diode is located on, and extendsparallel to, a major surface of the support, and emits light parallel tothe major surface of the support, and the integrated back light unitfurther comprises a waveguide that directs light from the at least onelight emitting diode toward the front side of the support and to thefirst face of the polarizer; and optically connecting display comprisingan array of pixels to a second face of the polarizer, wherein the firstface of the polarizer and the second face of the polarizer are notparallel; and wherein the polarizer is configured to direct light fromthe integrated back light unit to the display.
 11. The method of claim10, wherein the first face and the second face make an approximately 90°angle.
 12. The method of claim 10, wherein the integrated back lightunit provides red, blue and green light.
 13. A method of projecting animage, comprising: providing plural colors of light from an integratedback light unit to a first face of a polarizer, wherein the integratedback light unit comprises at least one light emitting diode mounted on asupport in a side-emitting configuration that provides illumination to afront side of the support, wherein the at least one light emitting diodeis located on, and extends parallel to, a major surface of the support,and emits light parallel to the major surface of the support, and theintegrated back light unit further comprises a waveguide that directslight from the at least one light emitting diode toward the front sideof the support and to the first face of the polarizer; providing lightfrom a second face of the polarizer to an array of pixels of a displaythat faces the second face of the polarizer; and projecting an imagegenerated by reflection of the light from the array of pixels throughthe polarizer.
 14. The method of claim 13, wherein the first face of thepolarizer and the second face of the polarizer are not parallel.
 15. Themethod of claim 14, wherein the first face and the second face make anapproximately 90° angle.
 16. The method of claim 13, wherein the imageis projected from the array of pixels through the polarizer onto asurface or into a space between surfaces.
 17. The method of claim 13,wherein the integrated back light unit provides red, blue and greenlight from a plurality of red, blue and green emitting light emittingdiodes.
 18. The method of claim 13, wherein the array of pixelscomprises an array of liquid crystal or DLP mirror pixels.
 19. Themethod of claim 13, wherein the display comprises an image projectiondisplay.
 20. The method of claim 19, wherein the image projectiondisplay comprises a wearable display, a pico display or a head updisplay.
 21. The method of claim 10, wherein the waveguide comprisesparticles of a wavelength converting material embedded within anoptically transparent material.
 22. The method of claim 13, wherein thewaveguide comprises particles of a wavelength converting materialembedded within an optically transparent material.
 23. The system ofclaim 1, wherein the waveguide comprises a light guiding plate which islocated on the major surface of the support and extends parallel to themajor surface of the support.
 24. The method of claim 10, wherein thewaveguide comprises a light guiding plate which is located on the majorsurface of the support and extends parallel to the major surface of thesupport.
 25. The method of claim 13, wherein the waveguide comprises alight guiding plate which is located on the major surface of the supportand extends parallel to the major surface of the support.